Size and weight is a big decision factor when you are trying to find the ideal camera for your needs.
In this section, We are going to illustrate Panasonic ZS1 and Olympus E-P3 side-by-side from the front, back and top in their relative dimensions. Panasonic ZS1 has external dimensions of 103 x 60 x 33 mm (4.06 x 2.36 x 1.3″) and weighs 229 g (0.50 lb / 8.08 oz) (including batteries). Olympus E-P3 has external dimensions of 122 x 69 x 34 mm (4.8 x 2.72 x 1.34″) and weighs 369 g (0.81 lb / 13.02 oz) (including batteries).
Below you can see the front view size comparison of Panasonic ZS1 and Olympus E-P3. Panasonic ZS1 is clearly the smaller of the two cameras. Its body is 19mm narrower, 9mm shorter and 1mm thinner than Olympus E-P3. As you can tell, actually this is not a fair size comparison since Panasonic ZS1 has a built-in lens but Olympus E-P3 doesn't. Once you put a lens on E-P3, its thickness will increase significantly.
Here is the back view size comparison of Panasonic ZS1 and Olympus E-P3.
Weight is another important factor especially when deciding on a camera that you want to carry with you all day.
Panasonic ZS1 is significantly lighter (140g ) than the Olympus E-P3 which may become a big advantage especially on long walking trips.
Again, this comparison may not be very useful in real life as we are comparing the weight of a camera with a built-in lens to the body-only weight of an interchangeable lens camera. Once you put a lens on E-P3, the total kit will weigh much higher.
Unfortunately neither Panasonic Lumix DMC-ZS1 (Lumix DMC-TZ6) nor Olympus PEN E-P3 provides any type of weather sealing in their body, so you have to give extra care especially when you are shooting outdoors. If weather sealing is a must-have feature for you, check these sections: Top Compact Cameras with Weather Sealing Top Mirrorless Cameras with Weather Sealing
LCD Screen Size and Features
Olympus E-P3's 3" LCD screen is slightly larger than Panasonic ZS1's 2.7" screen.
Unfortunately, both cameras has fixed screens so they don't tilt or flip in directions.